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Efficacy of Bacillus thuringiensis Berliner (Bt) and malathion 50 EC on leaf folder and the predatory coccinellid beetle Menochilus sexmaculatus was assessed in paddy field cultivar on Swarna mashuri during 2005-2008 at Raiganj, Uttar Dinajpur, West Bengal. Bt and malathion were applied at vegetative and early tillering stage. Control field was treated with the same volume of water. Malathion was found superior in suppressing leaf folder population at first application than the second. Numerically, at post application counting, maximum leaf folder population (122.21 moths/trap and 13.09 larva / 4m) with lowest grain yield (19.72 q/ha) was noted in control. Least pest incidenče (62.87 moths/trap and 1.02 larval individuals/4m) with maximum grain yield (34.27 q/ha) was noted when malathion was applied (a) 1.0kg/ha. This result was statistically at par with the application of Bt formulation (a) 3.0 kg/ha. Overall impact of malathion on predatory coccinellid population was found detrimental in suppressing the population to an extent of 59.36-83.82% and 54.42-74.22% during first and second phase of applications, respectively. Bt formulation had no significant repression effect on beetle population recording 0.49-3.48% and 0.38-1.86% in the first and second round, respectively. Bt formulation (a) 3.0 kg/ha was found economical and environmentally prudent.